Disturbance observer based robot control with applications to force control

This dissertation examines the use of a robust control structure, the disturbance observer, as a component of robot control algorithms. Special emphasis is placed on the development of force control algorithms. Robotic deburring is investigated as a potential application of the developed force controller.; The disturbance observer can be used to linearize the nonlinear robot dynamics. It is demonstrated that the disturbance observer makes it possible to use linear control techniques, such as the Zero Phase Error Tracking Controller (ZPETC), that rely heavily on the controlled plants linearity. This feature of the disturbance observer is exploited to design a robust motion control algorithm for a general manipulator based on a linear motion controller. This disturbance observer based motion controller is shown to provide better tracking accuracy than that of a common adaptive algorithm.; The stability of a disturbance observer based control algorithm termed the Acceleration Tracking Controller (ATC) is examined through a comparison to the passivity-based robot control algorithms. Although the robot control algorithms determined using the disturbance observer based approach and the passivity-based approach have been studied as two separate types of robot control algorithms, it is shown that the passivity-based approach is in fact a subset of the ATC. In addition, an adaptive term is added to the ATC to improve its performance and to guarantee robust stability to parameter variations.; The disturbance observer based ATC is then used to realize a Hybrid Impedance Controller. The impedance control simulation results demonstrate the effectiveness of the disturbance observer to enforce a desired impedance relationship. It is shown that the ATC can be designed in either joint or constraint coordinates, but the task-space based ATC is limited by its time-varying nature.; Finally, it is shown that a disturbance observer based Hybrid Impedance Controller (HIC) can be used effectively in interacting with an external object in the robot's workspace. Surface following experiments show that this controller can be used to maintain a constant normal force against a constraint surface. Robotic deburring experiments show that this controller can maintain a consistent depth of cut for chamfering an aluminum workpiece.